This invention pertains to centrifugal pump impellers, and to such impellers in combination with centrifugal pump housings, used to pump liquids which contain solid pollutants, and in particular to such impellers which cooperate with the pump housings to supply the pumped liquid to a cooling system which keeps the pump motor from overheating.
A common centrifugal pump is the so-called submersible pump in which the pump and its electric motor comprise a unit which is submersed in the pumped liquid. In this, the motor is normally cooled directly by the surrounding, pumped liquid. If, however, the level of the liquid decreases, so that the motor is surrounded by air, the cooling may be insufficient. Therefore, the motor is provided with an internal cooling system which uses the pumped liquid. An example of such an arrangement is shown in the Swedish Patent No. 367 465 (U.S. Pat. No. 3,371,613).
As the pumped liquid often contains solid pollutants, the aforesaid patent teaches the use of a narrow slot, arranged between the impeller and the pump housing, through which comparatively clean liquid is fed into the cooling liquid area between the pump and the motor. The cooling liquid is circulated by means of vanes arranged on the back of the impeller. The slot prevents pollutants from entering into the cooling liquid area and, thus, diminishes the possibility of clogging the cooling channels disposed about the motor.
Further, according to the aforesaid patent, vanes are arranged within the cooling jacket of the motor to convey the cooling liquid upwardly to effect a cooling of the entire motor.
It has been observed that, at pump start-up, air bubbles can collect within the cooling liquid area at the back of the impeller, i.e., between the pump housing and the impeller. As a consequence, the vanes in the cooling jacket may not be able to ingest the cooling liquid and no circulation of the latter can result.